For all types of substrates, magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and is now working toward densities of 800 Gbits/in2. Generally, PMR media may be partitioned into two primary functional regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional perpendicular magnetic recording disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
Typically, higher areal densities are typically achieved with well-isolated smaller grains in the PMR layer. A higher magnetocrystalline anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise.
With the advent of heat-assisted magnetic recording (HAMR) media, areal densities of 900 Gbits/in2 and higher using PMR technology has been realized. This is because HAMR media comprises of a magnetic compound, such as an FePT alloy, that has a higher magnetic stability than PMR technology using non-HAMR media (e.g., CoPt). However, because the HAMR media comprises of such higher-stability magnetic compounds, HAMR media requires that heat be applied to it before changes its magnetic orientation can be changed. Typically, when PMR technology magnetically records data to HAMR media, it first uses a heating element, such as a laser, to increase the temperature of the recording location on the media, in order to lower the location's high magnetic anisotropy constant (Ku) sufficiently to allow a change to its magnetic orientation (i.e., record data).
FIG. 2 illustrates a cross-sectional view of an exemplary heat-assisted magnetic recording (HAMR) media comprising a hard magnetic recording layer 205, a soft magnetic underlayer (SUL) 210, a heatsink layer and non-magnetic interlayer 215 between the hard magnetic recording layer 205 and soft magnetic underlayer 210, and a bottom substrate 225. The hard magnetic recording layer 205 illustrated is a L10 layer made of iron platinum (FePt), a magnetic compound known to have a high magnetic anisotropy constant (Ku). Other suitable compounds for the hard magnetic layer include iron platinum alloys (FePtX), such as FePtCu, FePtAu, FePtAg, and FePtNi. It has been discovered that certain dopants, such as carbon (resulting in FePtX:C), when added to a iron platinum alloy of a hard magnetic recording layer, results in small grain size, granular microstructure, high magnetocrystalline anisotropy, high coercivity, good texture and ordering, and lower ordering temperature, all of which are desirable properties for HAMR media.
Unfortunately, in order to provide strong magnetic signal for the reader sensor detection and high signal-to-noise ratio (SNR) in the recording process, HAMR media require a relatively thick hard magnetic recording layer, preferably a thickness above 5 nm. This is particularly problematic for HAMR media that utilize carbon doped iron platinum alloy (FePtX:C) for its hard magnetic layer, as typically a FePtX:C hard magnetic layer having a thicknesses beyond 5-6 nm results in the formation of two or more layers of FePtX:C. This is clearly shown in FIG. 3A-3C, where FIG. 3A shows a FePt:C recording layer (303) of ˜4.6 nm forming a single layer, where FIG. 3B shows a FePt:C recording layer (306) of ˜7 nm starting to form a second layer, and where FIG. 3C shows a FePt:C recording layer (309) of ˜9.8 nm forming two layers (312 and 315). When more than a single layer forms within the hard magnetic layer, properties required of the HAMR, such as high coercivity, begin to degrade. For example, FIG. 4 illustrates how coercivity for the examples provided in FIGS. 3A-3C begins to degrade as the thickness of the FePt:C recording layer increases.